Hot-testing of IC engines outside of a vehicle (extra-vehicular) is known generally, being used mainly in the testing of newly manufactured, production line engines and in the testing of overhauled or repaired engines. The term hot-test refers to testing the engine with ignition to determine basic dynamic engine performance. At present, the actual tests performed during the engine hot-test involve the most basic test criteria and rely almost entirely on the hot-test operation for diagnosing base-line engine performance. Although the tests may involve measurement of basic engine timing, in general the pass/fail acceptance standards are based on what the operator perceives of the engine running characteristics, such as the inability to start or to maintain engine speed, or the sound of the engine while running. These tests do provide suitable pass/fail criteria for gross engine malfunctions, however, it is impossible, except to the most experienced operator, to provide even simple diagnosis of the cause of the engine poor performance.
In the first instance, the inability to provide quantitative measurements of engine performance and acceptance, results in the acceptance of marginal engines in which the actual failure occurs sometime later as an infant mortality, perhaps after installation in the vehicle. Conversely, the rejection of an engine based on the present qualitative standards may be unwarranted in many instances, resulting in the unnecessary recycling of the engine through some type of repair facility, where with more extensive testing the apparent fault may be corrected with a minor engine adjustment. Therefore, it is desirable to establish an accurate quantitative analysis testing procedure which with measurement of selected engine parameters may provide for accurate pass/fail determination.
In general, the present state of the art of IC engine diagnostics includes the use of a number of different measurable engine parameters which in one way or other are useful in providing information as to engine performance. One such parameter is sparkplug voltage which provides an indication of the performance of the engine's secondary ignition circuit in addition to particular cylinder ignition faults. At present, however, measurements of sparkplug voltage signals are provided on a single cylinder one-at-a-time basis, such that each cylinder's spark waveform is measured individually and compared with acceptable tolerances for peak KV amplitude and spark duration. Identification of measured spark signal with the associated cylinder is provided either by direct measurement of the spark signal at the cylinder sparkplug, or if sensed at the secondary of the engine ingition coil, by synchronization of the spark sample with an engine timing event. In either case measurements are provided on an individual basis without benefit of comparison of a particular cylinder's spark waveform with the spark signals provided to the remaining cylinders within the same engine cycle. Since the existence of an ignition fault in one cylinder may affect, to one extent or another, the sparkplug voltage signal provided to one or more other cylinders it is preferred to compare each of the cylinder spark signals with the others occurring within the same engine cycle. This permits the measurement of the relative performance of each cylinder in comparison with the remaining cylinders under simultaneously equal test conditions.
Similarly, the present methods of measuring each cylinder's spark signal makes it difficult to detect intermittent firing of a given cylinder since the spark signal measurement is provided as an average of the cylinder's spark signal over recurring engine cycles. By providing for the detection of intermittent spark, or the indication of relative ignition efficiency of each cylinder within each of a number of engine cycles, both present and imminent ignition system faults may be detected.